The U.S. would even help the North Korean economy if it takes "bold action to quickly denuclearize", the top U.S. diplomat added.

"The key is for the North Korean leader to decide", Abe told the Fuji Television network.

Pompeo has had two recent meetings with Kim to prepare for the summit and, last weekend, to negotiate the release of three Korean-Americans held in the North's jails.

North Korea has long seen its nuclear program as key to its survival, and it's not certain how honest Kim Jong-un is about giving up his nuclear arsenal.

"We'll require a robust verification program, one that we would undertake with partners around the world which would achieve that outcome", he warned.

"I think there is complete agreement about what the ultimate objectives are", he said, though declined to offermore detail. By doing so, they said, Washington is "prepared to work with Pyongyang to achieve prosperity".

In exchange for that USA demand - one that many believe North Korea isn't seriously considering - the U.S.is willing to offer economic assistance, Pompeo said, promising "a future brimming with peace and prosperity".

Until then, however, the global sanctions will remain in place, Foreign Minister Kang said.

But American officials have said Kim has signaled a willingness to move toward denuclearization amid a softening of relations between the USA and North Korea in recent weeks.

While Kang sought to assure reporters that the USA and South Korea are unified on the matter, she was slightly more moderate on the possibility of relief, saying sanctions must remain in place "until we see visible, meaningful action taken by North Korea on the denuclearization track".

"The release of the three detainees does not absolve the regime of a history of human rights abuses that must be the topic of any discussion going forward on normalising political relations between the United States and North Korea".

Regarding the question about Iranian Foreign Minister Zarif's visit to China on Sunday, Shuang said the two countries have maintained close communication and exchanges.

The secretary of state addressed concerns that the USA and North Korea have different objectives in mind when considering denuclearization, prompting doubts that the Kim regime will actually be willing to give up the weapons it has already built.

"We would like to express our deep appreciation to the United States government, President Trump, Secretary Pompeo, and the people of the United States for bringing us home", the detainees said in a statement as they flew to Washington. "It is extremely important for North Korea to normalize diplomatic relations with Japan to walk along the right track as part of global society, while accepting its requirements".

Pompeo noted the enormity of the challenge, but said, "Chairman Kim and I had an opportunity to have a good, sound discussion on [that], so that I think we have a pretty good understanding between our two countries on what the shared objectives are".

He said he had had good conversations with Kim, who he found to be a focused and rational interlocutor.

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